In June 2012, 3GPP hosted a workshop that involved radio access techniques in the future.
In the workshop, many companies proposed an “enhanced small cell” as one of the radio access techniques in the future (see Non-patent document 1).
Particularly, a “macro-assisted cell (or a phantom cell)” was proposed in addition to the existing “stand-alone cell” (see Non-patent document 2).
The followings are characteristics of a mobile communication system in which the “macro-assisted cell” is located.
The mobile communication system is configured to split C-plane and U-plane between a macro cell and the “macro-assisted cell.”
As a result, the macro cell can maintain excellent mobility and connectivity by supporting the C-plane (RRC signaling) at a low frequency used in a conventional mobile communication system.
In the meantime, the “macro-assisted cell” can provide communication with fast throughput as well as flexible and efficient cost and power by performing the communication of the U-plane (user data) while using a high frequency where a broadband is available.
Here, unlike the existing cell, the “macro-assisted cell” is not required to transmit a reference signal common to cells, a synchronization signal, or broadcast information (MIB/SIB). In this regard, the “macro-assisted cell” is a cell with a different concept from that of the conventional cell.
Meanwhile, in the mobile communication system in which the “macro-assisted cell” is located, the C-plane and the U-plane are generally split between the macro cell and the “macro-assisted cell” as described above. Specifically, the macro cell transmits the C-plane while the “macro-assisted cell” transmits the U-plane. Such assignments of the C-plane and the U-plane may be strict or not.
For example, part of the U-plane may be transmitted by the macro cell. To be more precise, since connectivity or stability is important in a “real time service” such as a voice service, the macro cell may transmit such a “real time service” also in consideration of quality during high-speed movement.
On the other hand, concerning the C-plane as well, control information that is important in establishing the communication may be transmitted by the macro cell while other less important control information may be transmitted by the “macro-assisted cell.”
In the above-described mobile communication system, a mobile station UE can establish connection to both of the macro cell and the “macro-assisted cell” at the same time.
Note that the “macro-assisted cell” is a cell which can be operated only within the coverage of the macro cell.